1. Field of the Invention
The present invention relates generally to a torque transfer device and, more particularly, to a torque transfer device employing a particle clutch and an electromagnetic clutch.
2. Description of the Related Art
Magnetically operated devices for transferring torque are well known in the art. One known magnetically operated device for transferring torque is an electromagnetic friction clutch. Electromagnetic friction clutches are commonly used in the automotive field for engaging and disengaging belt-driven engine accessories, such as an air conditioning compressor. An electromagnetic friction clutch is typically provided between the belt and the driven accessory to selectively transfer torque from the drive belt to an input shaft of the accessory.
Electromagnetic friction clutches are engaged by energizing a coil to create a magnet field. In one known electromagnetic friction clutch, the magnetic field forces a spring-biased friction plate of an input member to impact and frictionally engage an output member. Because electromagnetic friction clutches operate in an xe2x80x9cON-OFFxe2x80x9d manner, the initial impact of the friction plate against the output member creates an annoying sound that can be heard by occupants of the vehicle. Furthermore, the initial impact of the friction plate against the output member demands a significant amount of torque from the engine, which may be undesirably perceived by the occupants of the vehicle.
Another magnetically operated torque transferring device that is well known in the art is a magnetic particle clutch. A magnetic particle clutch offers advantages such as low vibration torque transfer, the ability to operate in a slip condition and controlled torque transfer. Unlike an electromagnetic friction clutch, a magnetic particle clutch can be gradually engaged to provide a highly controllable, xe2x80x9csoftxe2x80x9d and substantially noise-free engagement. However, the torque transfer density of a magnetic particle clutch is generally smaller than an electromagnetic friction clutch. In other words, a magnetic particle clutch will transfer less torque per unit area than an electromagnetic friction clutch.
Therefore, it would be desirable to provide a magnetically operated torque transferring device that combines the control and xe2x80x9csoftxe2x80x9d engagement capabilities of a magnetic particle clutch with the relatively high torque transfer density of an electromagnetic friction clutch.
In accordance with the principles of the present invention, a torque transfer device is provided that includes an input member for receiving torque from an external source. An output member is disposed radially inward of the input member to define a first torque transferring region therebetween. A second torque transferring region is also disposed between the input member and output member. A source of magnetic flux is operable to provide a first level of magnetic flux that transfers torque between the input and output members by activation of the first torque transferring region. The source of magnetic flux is also operable to provide a second level of magnetic flux that transfers torque between the input and output members by activation of both the first torque transferring region and the second torque transferring region.
In a preferred embodiment of the present invention a torque transfer device is provided that includes a particle clutch having an input drum, an output drum and a magnetically reactive medium. The input drum receives torque from an external source. The input drum has a cylindrical portion extending from a base portion and also has regions of high magnetic permeability and low magnetic permeability. The output drum has a cylindrical portion extending from a base portion and is disposed within the input drum to define a first gap along the cylindrical portions of the input drum and output drum that contains the magnetically reactive medium. The output drum has regions of high magnetic permeability and regions of low magnetic permeability.
The torque transferring device further includes a friction clutch having a friction plate disposed adjacent to one of the base portion of the output drum and the base portion of the input drum to define a second gap therebetween. At least one biasing member is coupled to the friction plate and to the other of the base portion of the input member and the base portion of the output member for maintaining the second gap when the friction plate is disengaged. The torque transfer device also includes a source of magnetic flux that is operable to transition the torque transferring device among a non-engaged state where neither the particle clutch nor the friction clutch are engaged, a partially engaged state where the particle clutch is at least partially engaged, and a fully engaged state where the particle clutch and friction clutch are engaged.
Among other advantages, the torque transfer device substantially eliminates or reduces the xe2x80x9chardxe2x80x9d or sudden engagement of conventional electromagnetic clutches. Another advantage is that the torque transfer device substantially eliminates or reduces the undesirable engagement sound that is characteristic of conventional electromagnetic clutches. Still another advantage is that the torque transfer device allows for a gradual, controlled engagement without sacrificing the ability to transfer relatively high levels of torque.